A large amount of technological interest has been focused on rare earth-iron-boron alloys (e.g., 26.7 weight % Nd-72.3 weight % Fe-1.0 weight % B) as a result of their promising magnetic properties for permanent magnet applications attributable to the magnetically hard Nd.sub.2 Fe.sub.14 B phase. Commercial permanent magnets of these alloys having anisotropic, aligned structure exhibit high potential energy products (i.e., BHmax) of 40-48 MGOe while those having anisotropic, non-aligned structure exhibit potential energy products of 5-10 MGOe. Such energy product levels are much higher than those exhibited by Sm-Co alloys (e.g., SmCo.sub.5 and Sm.sub.2 Co.sub.17) previously regarded as having optimum magnetic properties. The rare earth-iron-boron alloys are also advantageous over the SmCo alloys in that the rare earth (e.g., Nd) and Fe are much more abundant and economical than Sm and Co. As a result, rare earth-iron-boron permanent magnets are used in a wide variety of applications including, but not limited to, audio loud speakers, electric motors, generators, meters, scientific instruments and the like.
Several distinct processes have been disclosed to fabricate fully dense, permanent magnets from Nd-Fe-B alloys. One process involves forming a rapidly solidified, nearly amorphorous ribbon, mechanically comminuting the ribbon to form flake particulates and then hot pressing and aligning the flake particulates at elevated temperature in a die cavity. Another process involves grinding the Nd-Fe-B alloy into fine powder, aligning the powder in a magnetic field during cold pressing, and sintering the cold pressed powder to near full density. These processes have been employed to make aligned (i.e., anisotropic) permanent magnets.
Resin bonding of rapidly solidified ribbon of Nd-Fe-B alloys has been proposed by R. W. Lee in an article entitled "Hot-pressed Neodymium-iron-boron Magnets", Appl. Phys. Lett. 46: pp. 790-791 (1985) as a technique for fabricating isotropic permanent magnets. In order to make resin bonded magnets from rapidly solidified, melt-spun ribbon, it is necessary to comminute the friable ribbon into flake particulates and then to compact the particulates under pressure to a desired shape of simple geometry in a compression molding die. The voids of the compact are typically filled with a liquid polymer, such as epoxy and the like, to form a bonded magnet.
It is an object of the present invention to provide a method of making isotropic permanent magnets from rare earth-transition metal alloys using a unique alloy powder/binder feedstock blend or mixture that facilitates molding of the mixture at relatively low temperatures to previously unachievable or difficult-to-achieve complex shapes.
It is another object of the present invention to provide a method of making isotropic permanent magnets from rare earth-transition metal alloys wherein low viscosity binder-assisted molding permits relatively low temperature molding of the feedstock blend or mixture having optimum volume loading of atomized alloy powder for a particular application.
It is still another object of the present invention to provide isotropic permanent magnets molded from the alloy powder/binder feedstock blend or mixture.